136 lines
2.9 KiB
C
136 lines
2.9 KiB
C
#define _GNU_SOURCE
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#include <stdlib.h>
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#include <unistd.h>
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#include <stdio.h>
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#include <errno.h>
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#include <string.h>
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#include <linux/limits.h>
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#include <sys/types.h>
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#include <sys/wait.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <signal.h>
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#include <setjmp.h>
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#include <sched.h>
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#include <signal.h>
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/* All arguments should be above stack, because it grows down */
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struct clone_arg {
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/*
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* Reserve some space for clone() to locate arguments
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* and retcode in this place
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*/
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char stack[4096] __attribute__ ((aligned(8)));
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char stack_ptr[0];
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jmp_buf *env;
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};
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static int child_func(void *_arg)
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{
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struct clone_arg *arg = (struct clone_arg *)_arg;
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longjmp(*arg->env, 1);
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}
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#define pr_perror(fmt, ...) fprintf(stderr, "nsenter: " fmt ": %m\n", ##__VA_ARGS__)
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// Use raw setns syscall for versions of glibc that don't include it (namely glibc-2.12)
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#if __GLIBC__ == 2 && __GLIBC_MINOR__ < 14
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#define _GNU_SOURCE
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#include "syscall.h"
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#ifdef SYS_setns
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int setns(int fd, int nstype)
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{
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return syscall(SYS_setns, fd, nstype);
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}
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#endif
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#endif
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static int clone_parent(jmp_buf * env) __attribute__ ((noinline));
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static int clone_parent(jmp_buf * env)
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{
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struct clone_arg ca;
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int child;
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ca.env = env;
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child = clone(child_func, ca.stack_ptr, CLONE_PARENT | SIGCHLD, &ca);
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return child;
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}
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void nsexec()
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{
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char *namespaces[] = { "ipc", "uts", "net", "pid", "mnt" };
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const int num = sizeof(namespaces) / sizeof(char *);
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jmp_buf env;
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char buf[PATH_MAX], *val;
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int i, tfd, child, len;
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pid_t pid;
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val = getenv("_LIBCONTAINER_INITPID");
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if (val == NULL)
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return;
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pid = atoi(val);
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snprintf(buf, sizeof(buf), "%d", pid);
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if (strcmp(val, buf)) {
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pr_perror("Unable to parse _LIBCONTAINER_INITPID");
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exit(1);
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}
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/* Check that the specified process exists */
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snprintf(buf, PATH_MAX - 1, "/proc/%d/ns", pid);
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tfd = open(buf, O_DIRECTORY | O_RDONLY);
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if (tfd == -1) {
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pr_perror("Failed to open \"%s\"", buf);
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exit(1);
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}
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for (i = 0; i < num; i++) {
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struct stat st;
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int fd;
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/* Symlinks on all namespaces exist for dead processes, but they can't be opened */
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if (fstatat(tfd, namespaces[i], &st, AT_SYMLINK_NOFOLLOW) == -1) {
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// Ignore nonexistent namespaces.
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if (errno == ENOENT)
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continue;
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}
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fd = openat(tfd, namespaces[i], O_RDONLY);
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if (fd == -1) {
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pr_perror("Failed to open ns file %s for ns %s", buf,
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namespaces[i]);
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exit(1);
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}
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// Set the namespace.
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if (setns(fd, 0) == -1) {
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pr_perror("Failed to setns for %s", namespaces[i]);
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exit(1);
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}
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close(fd);
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}
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if (setjmp(env) == 1) {
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// Finish executing, let the Go runtime take over.
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return;
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}
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child = clone_parent(&env);
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if (child < 0) {
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pr_perror("Unable to fork");
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exit(1);
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}
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len = snprintf(buf, sizeof(buf), "{ \"pid\" : %d }\n", child);
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if (write(3, buf, len) != len) {
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pr_perror("Unable to send a child pid");
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kill(child, SIGKILL);
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exit(1);
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}
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exit(0);
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}
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